23 LITHOLOGICAL UNIT THICKNESS APPROACH FOR DETERMINING INTACT ROCK STRENGTH (IRS) OF SLOPE FORMING ROCK MATERIAL OF CROCKER FORMATION Ismail Abd Rahim, Sanudin Hj. Tahir, Baba Musta & Shariff A. K. Omang School of Science and Technology, Universiti Malaysia Sabah, 88999 Kota Kinabalu, Sabah, Malaysia ABSTRACT. The Intact Rock Strength (IRS) of slope forming rock material of the heterogeneous Crocker Formation has been determined using “Lithological Unit Thickness” approach in order to evaluate the slope stability. Four slopes in CPSB Stone Quarry were selected in this study namely slope B1, B2, B3, and B4. The “Lithological Unit Thickness” approach in this paper consists of slope geological mapping, slope geometry, lithological thickness measurement, petrographic analysis, intact rock strength testing and modeling. The intact rock strength was measured using Unconfined Compressive Strength test and Point Load test. The results show that the estimation of intact rock strength of the slope forming rock material by 'lithological unit thickness' approach is more representative and the value for slopes B1, B2, B3 and B4 are 129 MPa, 108 MPa, 117 MPa and 148 MPa, respectively. The intact rock strength for the slopes forming rock material in the study area can also be classified as 'strong' rock masses. KEYWORDS. Lithological unit, Intact Rock Strength, slope stability, Crocker Formation INTRODUCTION The study area is located in CPSB Stone Quarry, Tamparuli, Sabah, Malaysia (Figure 1). In this study, the quarry faces have been divided into four (4) sections denoted as B1, B2, B3 and B4 (Figure 2). Geology of the area is underlain by the Crocker Formation of Late Eocene to Early Miocene age. The Crocker Formation is a deep marine environment of flysch typed deposit. The sedimentary rock is characterized by rhythmic alteration of sandstone and fine-grained (pelitic) or shale layers. The Crocker Formation is also divided into sandstone facies, sandstone-shale interbedded facies and shale facies. The overall thickness is very large, even though it may have reduced considerably by erosion and thrusts. Intact rock strength (IRS) is a basic rock property. IRS determines the strength of the intact rock block material and as such governs partially the strength of a rock mass. Standard determination of the IRS is by means of an Unconfined Compressive Strength (UCS) test. IRS is also an important parameter used in most of the rock mass classification systems, analytical and numerical calculations (Hack & Huisman, 2002). BORNEO SCIENCE 25: SEPTEMBER 2009